My name is Professor Ian Duncan and I would like to rap for you. Drop a beat! My name is Ian Duncan and I'm here to say, I'm going to rap to the beat in a rapping way! I've got a real big penis and I drink lots of tea...

Dr. Ian Duncan (portrayed by actor/comedian John Oliver) is a psychology professor at Greendale Community College. Ian was born in Birmingham, England and grew up on 52nd street in the Islington district of London (although this is actually a writing error as confirmed by Dan Harmon, as British streets are not numbered)[1]. His mother was a native of Lincolnshire, from a town called Scunthorpe where she worked as a whore at a Stansbury pub with her thumb-less sister. Duncan's father was absent for much of his childhood and it's alluded that he left England shortly after his parents divorced. He came to America with his grandfather when he was very young and eventually became a psychologist. He was hired by Greendale Community College and was made the head of its psychology department. Duncan started drinking heavily and his addiction caused him to run into some legal problems. At one point during driving drunk, he tried to order chalupas from an emergency call box on a highway. Jeff Winger was still a practicing attorney at the time and managed to get Ian off the hook. The two became drinking buddies, and, years later when Jeff enrolled at Greendale, he unsuccessfully tried to call upon the favor Ian owed him. Although Duncan was present during Jeff's first and second year at school, he took a leave of absence before his friend graduated. He spent that time back in England taking care of his mother who was ill. Duncan returned to his position at Greendale a few years later and reconnected with Jeff, who had since become a member of the faculty.

Duncan's turbulent upbringing after being abandoned by his father was possibly a large factor in his subsequent abuse of alcohol. His on-again, off-again drinking problem has greatly affected his personal and professional life ("Pascal's Triangle Revisited"). His addiction got so bad he frequently showed up to his classes inebriated ("The Psychology of Letting Go"). When he is actually sober, he can be a very good psychologist and capable of keen insight. Whilst at times he lectured Jeff on his ethical choices, he is capable of making a few morally ambiguous decisions himself. This included attempting to exploit Abed's mental breakdown for a book deal ("Abed's Uncontrollable Christmas") and taking an Anthropology class he was substituting for and turning it into a BYOB party ("Applied Anthropology and Culinary Arts") where he frequently "taught" by allowing the class to watch viral videos on youtube. However, on occasion he has demonstrated the ability to do what's right despite the pressure to do the opposite. This was shown when he refused to help Jeff cheat on his tests ("Pilot") and when he didn't take advantage of Britta when she was emotionally vulnerable ("Bondage and Beta Male Sexuality").

At the start of the Fall 2009 semester at Greendale, Ian reunited with his old friend Jeff Winger, who was also his lawyer several years ago. Jeff was now disbarred due to him faking his qualifications and had enrolled at Greendale and asked Duncan to help him cheat to earn a legitimate degree. Duncan refused, unwilling to let Jeff continue in his dishonest ways, and unsuccessfully tried to teach him a lesson. In class, Duncan attempted to validate his "Duncan Principle" theory during one of his psych labs. However, he found his efforts hindered by an unexpected participant, Abed Nadir.

As part of the faculty he served on a tribunal made up of him, Dean Pelton, and Ben Chang to deal with Britta Perry who had cheated on her Spanish exam. The outcome had him volunteering to provide Britta free therapy to deal with her neuroses. Throughout the rest of the school year he had an antagonistic relationship with Ben Chang. By the end of the year Chang had been fired due to his teaching credentials having been faked. He was now a student at school and Duncan took great delight in taunting him. At the end of the year transfer dance Duncan found himself suspended by Dean Pelton when he made a drunk spectacle of himself. Since he was no longer officially on staff, Duncan got assaulted by Chang.

In 2009, Duncan was surprised to see his former lawyer and drinking buddy Jeff Winger enrolled at Greendale who had been disbarred until he earned a legitimate degree. Since Duncan owed Jeff for helping him get out of a D.U.I. charge years ago he asks that Ian get him every test answer that semester. Duncan balks at the request and tries to talk Jeff out of continuing his cycle of cheating to get ahead. After Jeff continued his demands Duncan made acquiesced but only on the condition that Jeff give him his Lexus. Ian also offered his own mini coup in exchange as part of the bargain so Jeff could have a vehicle. Jeff reluctantly agreed but afterwards discovered that Duncan just gives him an envelope of blank paper. Duncan was enjoying a glass of wine when a Jeff stormed into his office grabbed his car keys furious that Ian tried to teach him a lesson ("Pilot")

Duncan set up a psych lab and invited his top students to help prove his hypothesis, "The Duncan Principle." He posited that the longer a subject was left to wait for something the more dramatic the person's subsequent breakdown would be. Annie Edison managed to join Duncan's pupils in observing the experiment and recruited her friends Troy Barnes and Abed Nadir to participate. Duncan allowed her to start the lab once all the test subjects were gathered in one room. Ian was amused when one of the guinea pigs, Ben Chang, immediately went berserk and stormed out. As the hours passed the room emptied and only Abed remained which frustrated Duncan. Furious that Abed wouldn't leave, Duncan angrily criticized Annie for bringing him. His class then started to document his breakdown which made Duncan cancel the experiment and end the test lab ("Social Psychology").

Duncan served on a faculty tribunal alongside Dean Pelton and Ben Chang to deal with Britta Perry who cheated on a Spanish exam. The trial was being held in Borchert Hall at the edge of the swimming pool. Duncan and Chang's animosity towards each other reappeared as the two continually sniped at each other. During the recess they went off to clear the air between them. They argued all the way into the shower stalls in the men's locker rooms where Chang revealed he felt continually disrespected by Duncan. Their conversation was interrupted when they realized there was an overweight naked man showering in front of them. Back at the trial, Duncan and the rest of the tribunal were swayed by Jeff's argument that Britta should not be expelled for her actions. Duncan decided that she should instead be sentenced to a year's worth of therapy sessions conducted by him ("Advanced Criminal Law").

At the end of the school year Duncan was drunk again while attending the school's transfer formal. While at the dance he insulted the Dean which led to an immediate suspension. Chang at that point had been fired due to falsified credentials and enrolled himself at Greendale to earn a legitimate teaching degree. Duncan had mocked him earlier for his situation, but Chang couldn't retaliate physically or he could be kicked out of school. Once Ian was suspended, Chang took advantage of that fact to hit him in the face with a roll of quarters ("Pascal's Triangle Revisited").

In the study group's second year at a Greendale, Duncan is reinstated and finds himself unexpectedly teaching Anthropology. He is forced to take over the class after the original teacher, Professor June Bauer, is forced to go on sabbatical after attacking a student. Because he knows nothing about the subject, his teaching style was limited to showing the class various YouTube videos and assigning them dozens of dioramas to create. At Christmas time, Abed has a mental breakdown and Duncan is called in to try and therapize him. During the semester, he exploits the restraining order he put on Ben Chang, played piano for the Study Group when they briefly replaced the Glee Club (who died in a bus accident), and watched a (European) football game at Jeff's apartment on Valentine's Day. For a brief time he was sober but quickly fell off the wagon by the end of the year.

Professor Duncan is not seen during the 2011-2012 semester at Greendale but a book he authored is seen shown being held by Britta Perry who declared her major to be Psychology ("Contemporary Impressionists").

In the study group's fourth year at school, Professor Duncan didn't make an appearance. However, he is mentioned twice on two different occasions. When the group takes a hot air balloon ride that goes horribly wrong, Troy suddenly asks if anyone's noticed how long it's been since they've seen Duncan ("Intro to Felt Surrogacy"). Towards the end of the school year, the study group flashes back to their time before attending Greendale. Jeff recalls how after being disbarred he was inspired to go back and earn a legitimate degree after encountering Chang. He had been handing out flyers for the school and Jeff asked him if his old client Ian Duncan still worked there. Chang told Jeff that Duncan had tenure there while also referring to him as a "drunken limey"("Heroic Origins").

Ian Duncan returns to Greendale after some time away and joins the Save Greendale Committee. He reveals his absence was due to having to go back to England to take care of his sick mother. Upon his return he joins the investigation into the campus assailant called the "Ass Crack Bandit." He creates a useless psychological profile on the perpetrator and ends up becoming one of the bandit's victims. When Abed hosts a campus-wide game of Hot Lava, Duncan participates, hoping to win the $50,000 prize. He ends up being eliminated by Jeff and Annie when he tries to take Britta out of the game. Duncan and the Save Greendale Committee come up with a theme for the mid-term dance. He later asks Jeff's help in trying to woo Britta. He decides to not take advantage of a depressed Britta and hangs out with Jeff instead. When Jeff accidentally ends up in a coma he imagines Duncan as the cartoon character of "Xim Xam" in his G.I. Joe fantasy. Duncan and the committee celebrate prematurely after a city inspector gives Greendale a positive assessment. School board members Carl and Richie prepare to sell the school to the Subway corporation. Most of the staff, including Duncan, is laid off to make way for the new Subway employees. Buzz Hickey and Duncan commiserate over their unemployment and find they have a few things in common. Duncan meets up with the committee in a last ditch effort to prevent the sale of the school. They learn of a map which leads to a hidden computer lab which may hold the school founder Russell Borchert's lost wealth. While searching for the entrance way to the lab, Duncan electrocutes himself after grabbing exposed wires. He suffered some post traumatic confusion but later regained enough of his senses to celebrate with the rest committee after they succeed in saving the school.

In the second year of the "Save Greendale Committee", Abed attempts to clean up Greendale on his own. He is seen sweeping, replacing a light bulb, straightening a clock and polishing the name plate on the door of Professor Duncan's office ("Ladders").

At Greendale, he considers himself solely responsible for the success of the campus "Green Initiative," in which the faculty lounge in the human sciences building was painted a calming shade of green instead of the previous shade of beige. ("[[1]]")

Seen on a recurring basis in Season One and Season Two, Dr. Duncan didn't appear in Season Three or Four and was only briefly referenced in with his name appearing on the cover of a psychology text Britta had, and later Troy wondering aloud why they hadn't seen him in a while.

“Señor Chang, is there a word in Spanish for someone who used to pretend to be a professor but was a teacher, but wasn't actually a teacher, and is now a student? Is there a word for that? Oh. If it was in Spanish, you wouldn't know, would you?”— Ian Duncan